The relative importance of dietary patterns vs. macronutrient composition in affecting energy intake and body weight remains uncertain. In this study we propose to investigate the relative effects of dietary variety versus dietary fat on voluntary energy intake in adults. Specifically, we will quantify and compare the effects of typical ranges of variety and fat intakes in the American diet (based on U.S. national survey data) on voluntary energy intake. The primary hypotheses to be tested are (1) an increasing availability of entree/side/snack/dessert variety offered will significantly increase voluntary energy intake in a dose-response fashion when other dietary factors known to influence energy intake are held constant (including macronutrient composition, palatability and variety of other food items); and (2) the separate effects of dietary variety and dietary fat on energy intake will be similar. Healthy, weight stable men and women (n=96, aged 18-45 y, BMI 20-35 kg/m2) will be recruited for a 39-d study in which food is provided. Three levels of entree/side/snack/dessert variety will be offered at each of three levels of dietary fat intake, and the relative effects of these dietary manipulations on voluntary energy intake, independent of potentially confounding dietary factors, will be quantified. Subjects will be assigned to one of three BMI-matched groups that will be offered either 4, 8 or 12 entree/side/snack/dessert items/d at one of three fat intake levels (20, 35, or 50 % of energy) in each of three 13-d phases. All diets will be matched for palatability, fiber, protein content, and the variety of other food items, and also for energy density at each fat intake level. Daily voluntary energy intake will be measured and dietary compliance monitored by using measurements of 24-h urinary PABA and osmolar excretion rates. Other measurements include food and meal palatability, hunger, desire to eat, dietary disinhibition, energy expenditure, and body weight and composition. We anticipate that the results of this investigation will lead to a greater understanding of the relative importance of eating patterns vs macronutrient composition in the etiology of obesity, and more specifically, dietary variety versus dietary fat in determining energy intake. Most importantly, it will help lay a foundation for improved dietary recommendations concerning weight loss and prevention of excess weight gain in adulthood.